Took a few days of work getting the carb tune setup and making up some linkage parts BUT entirely worth it when I hit the pedal on a few test drives today! Project 2 Stage intended for hot and fun street and track performance uses a Holley 4224 carb in the rear position with a Holley 650 Vac. Secondary in front for primary clean street operation.

I transferred my primary metering block and jet plate from my well tuned secondary 650 carb to the new Holley 4224.
The metering block was setup as before with power valve and 68/68 jetting. Had to add the PV vac supply hole to the 4224 carb body along with drilling the carb body for screw in Air Bleeds to transfer same tune to the new 660 carb.

Due to the excellent fuel distribution of my dual quad intake the Mustang runs really well on just the front primary barrels of the front carb with no lean surge...just great throttle response and nice pull. So I setup the linkage to delay secondary carb action until past 40% of front carb throttle position. This gives excellent street usage without cycling the 4224 carb accelerator pump action which would kill the A/F ratio with excessive fuel being dumped.

End result is explosive engine response when you nail it in 1st thru 3rd gear in the TKO-600 trans. Plus the front carb vac. secondary is opening up for additional top end power.
Really LOVE the throttle response this thing has now!!

Cool setup. Does it work better than a standard single plane with a standard single carb setup?

For me it does! True a "RACE" Super Victor manifold might make more top end power BUT it won't run as strong as this or as lean while cruising or have same low end throttle response.
Who knows as I have both setups but like this the best and this dual quad setup did generate 480 HP and 505 Torque at the wheels at 5500 RPM with 475 FT. LBS starting at 2500 RPM...this before the rear carb swap.
With this new combo the engine gets up into the power quicker with the mechanical secondary carb in the rear.
Puts a big fat smile on you face too when that 660 takes over!

Wrap it all up in a 2900 lb. with driver and full tank of gas, the little Mustang LX coupe screams!

That is awesome! I am planning on taking my 660's and sending them to BLP and they are going to install their mini-annualar boosters and add metering blocks with PV's in both Primary and Secondaries so I can get decent part throttle gas mileage...

That is awesome! I am planning on taking my 660's and sending them to BLP and they are going to install their mini-annualar boosters and add metering blocks with PV's in both Primary and Secondaries so I can get decent part throttle gas mileage...

Andy

Well you really don't need a PV in the secondary....look at it as a 600/'650 with mechanical secondary action. What is killing you is the center squirt design pumping out un-needed fuel while secondary is closed and any more delay in opening secondary makes it worse.
Yes you do need a power valve in the primary metering block for clean part throttle operation.
Maybe use a vac. secondary 650 and see if your manifold combo will allow cruising on that carb.

Now the use of the 4160 style carbs is for limited space needs where a double pumper won't fit.

We are supposed to have some REAL cool October weather coming after the up coming hurricane moves thru the mid Atlantic area so I will get some GREAT less humid air for more tuning!

That's cool. I like how the linkage worked out. On the throttle, is that the only carb return spring?

The throttle cable has it's factory spring plus the return springs that are on each carb. Haven't had any issues with the setup over last couple years but I could add another to the linkage cross bar if needed.

Getting the linkage staging right took some time and had to make up a new extended length rod end plus slightly slot the end of that to get both carbs at full open. Had to also relocate the throttle link pin location closer to center to speed the action up in relation to front carb.

Since i am going running 1:1 linkages you must remember without PV's the secondaries will be overly rich at part throttle... I have had many people say "why don't you just put a set of double pumpers on it".. I want the old school look of the Center Squirters but have it perform like fuel injection!

I have those modified 1850's on it now but when I put those 660's on there... It was a completely different animal! The Mid range torque was explosive! So we came up with a plan to have my cake and eat it too!

Tried it anyway just to see what would happen as in most cases the screw in the Vac. Secondary link causes a huge bog. YES I put the screw in the front carb Secondary link!
To help situation I swapped the front carb accel pump cam from White to Pink 330 and set it in 1st hole for longer shot duration and kept same .025 nozzle.
Staged the "screw" to bring in secondary just after the rear 660 center squirter primary starts to open with it's accel pump working.

Took a few test drives and the engine is happy to gobble up the quicker front carb secondary action with no flat spot even works well at heavy mid throttle without fully opening up the carbs all the way...just hard strong pull.

Well at least there is no doubt that the front 650, which was Vac. Secondary is opening in tune with the 660! Let's call them both 660's as far as flow goes!

Yes this is considered a no no by most "professionals" but if conditons are ripe it might work sometimes!